Disposal of nuclear wastes is an important problem in the nuclear energy field today since many radioactive wastes must be stored for very long time periods to assure that no health hazard will be incurred. Low level nuclear combustible solid waste materials are a particular problem because of the relatively large bulk of materials associated with small amounts of contamination. Typical combustible solid waste materials of concern are those resulting from fuel fabrication operations, such as used rubber gloves, paper, rags, metals, glassware, brushes and various plastics. Of particular concern as well is the disposal of spent ion exchange resins from reactors, fuel fabrication plants and reprocessing plants (e.g. estimated to comprise from 500 to 800 cubic feet of material per year per nuclear reactor).
Present practice consists of packaging these solid waste materials in containers ranging from cardboard boxes lined with plastic bags to steel drums, then burying the packages in pits or trenches. This technique involves difficult and expensive handling of the scrap materials, transporting the packaged materials over roadways and finally storing the materials in monitored repositories or burial grounds. Potential release of contamination to the environment is possible as a result of rapid decay of the containers, or inadvertent combustion, etc. Moreover, in fuel reprocessing plants and fuel preparation plants, spent ion exchange resins contain significant amounts of plutonium as well as other fission products which may preclude direct burial of these resins.
Inasmuch as a large percentage of the contaminated solid waste material is simply light-weight, bulky combustible material, incineration of nuclear solid waste materials has been studied extensively, but it is subject to poor control of combustion, with attendant off-gas system difficulties and severe corrosion problems, coupled with rather expensive maintenance problems. Mechanical compaction of the solid waste material has also been studied extensively with volume reductions of two to ten-fold being achieved. In general, however, compaction and sorting of nuclear solid waste materials are moderately expensive in that special personnel protection devices are needed over and above normal protective equipment costs.
In another approach a process based on the use of sulfuric acid with a selenium catalyst has been used to reduce the volume of combustible low level radioactive waste. This process is described in "Treatment of Combustible, Solid, Low-Level Radioactive Waste at RISQ, the Danish Atomic Energy Commission Research Establishment," Proceedings of a Symposium on Practices in the Treatment of Low and intermediate Level Radioactive Waste, IAEA and ENEA, Vienna, December 1965. While this process affords volume reductions approaching 60, the process requires the use of a very toxic catalyst and apparently has poor control of the reaction rate.
It is therefore highly desirable, and a primary object of this invention, to have a controlled, safe, less expensive and more readily manageable form of treatment of low level nuclear combustible scrap material with suitable volume reductions.